Riser tensioner having oil collecting means

ABSTRACT

A riser tensioner that includes an oil collecting means and tensions a riser extending to the seabed from a drilling ship which drills for submarine resources. The riser tensioner further includes a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder, a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing, an oil collection passage extending from the head of the piston rod to an outside of the cylinder through the piston rod to allow oil leaking into the cylinder through the piston seal to be discharged from the cylinder to the outside of the cylinder through the oil collection passage, and an oil leakage detection sensor which detects oil leakage positioned on the head of the piston rod.

BACKGROUND

1. Technical Field

The present disclosure relates to a riser tensioner having an oil collecting means. More particularly, the present disclosure relates to a riser tensioner that includes an oil collecting means and tensions a riser extending to the seabed from a drilling ship which drills for submarine resources.

2. Description of the Related Art

Currently, with rapid industrialization and development of technology, stable production and supply of resources such as oil has become a crucial global issue due to increase in use of such resources.

For this reason, development of marginal fields or deep-sea oilfields, which have been ignored due to their low economic feasibility, has become economically feasible. Thus, offshore drilling vessels suitable for seabed oilfields have been developed together with seabed drilling technology.

Conventionally, submarine drilling is performed using submarine drilling rig ships or stationary platforms, which can sail only with assistance of tugboats and are anchored at one point at sea using moorings during drilling operation. Recently, submarine drilling is performed using a drillship which is fitted with advanced drilling apparatuses and has the same shape as a general ship so as to sail by its own power.

A rig ship or drillship (hereinafter, referred to as a drilling ship) fitted with a variety of drilling apparatuses to drill for oil or gas under the seabed is formed at the center thereof with a moon pool through which a riser or a drill pipe can move vertically for drilling operation.

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation.

A worker advances a riser 4 and a drill pipe 5 downwards through a moon pool 3 formed at the center of a drilling ship 1 using a lifting device provided to a derrick 2 to drill for submarine resources stored in an oil well 13 at bedrock 12 under the seabed 6.

The riser 4 is advanced to the seabed 6 to provide a path through which mud returns, prior to advancing the drill pipe 5 to the oil well 13. With the riser 4 installed between the drilling ship and the seabed, the drill pipe 5 is advanced downwards inside the riser 4 to the oil well 13 through a sea bottom stratum 11.

As such, when the riser 4 is advanced downwards to the seabed 6 or the drill pipe 5 is advanced to the oil well 13, short riser members of the riser or pipe members of the drill pipe 5 connected to each other are advanced downwards instead of using long riser members or drill pipe members connected to each other. On the seabed 6, a blowout preventer (BOP) 7 is installed to prevent high pressure from being transferred upwards along the drill pipe 5. In the sea bottom stratum 11, a casing 8 is secured by cement and a drill pipe 5 fitted with a drill bit 10 is inserted into the casing 8 to drill for submarine resources. To prevent the drill bit 10 from being excessively heated by heat generated by drilling operation of the drill bit 10 into the sea bottom stratum while facilitating the drilling operation through lubrication, mud 9 is inserted into the drill pipe 5. Then, the mud is discharged through the drill bit 10 and returns through the casing 8 and the riser 4. When drilling is completed, the drill pipe 5 is transferred to a drill floor through the moon pool 3, followed by disassembly for transportation to a storage location.

FIG. 2 is an enlarged view of Part A in FIG. 1.

The riser 4 may be divided into an upper riser 4 a and a lower riser 4 b with respect to a slip joint 20. Although the riser 4 extends from the drilling ship to the sea bottom, the slip joint 20 is provided to the middle of the riser 4 to allow the upper and lower risers 4 a, 4 b to move vertically with respect to each other in order to prevent vibration from being directly transferred from the upper riser 4 a connected to the drilling ship to the lower riser 4 b due to waves.

Since the distance of the riser 4 from the drilling ship to the sea bottom is several thousand meters and the mud passes through the riser 4, the total weight of the riser 4, the mud inside the riser and the BOP approaches several tons.

When the drilling ship is moved by waves and force generated due to movement of the upper riser 4 a connected to the drilling ship is directly transferred to the lower riser 4 b, the riser 4 having a length of several thousand meters may undergo buckling. To prevent such phenomenon, the drilling ship is provided with the slip joint 20 and a riser tensioner. The riser tensioner tensions the lower riser 4 b with a predetermined tensile force, thereby minimizing influence of movement of the drilling ship by waves on the riser 4.

The riser tensioner generally includes a support ring 30, a cylinder device 40, and a hydraulic device 50.

The support ring 30 connects the slip joint 20 to the cylinder device 40. The cylinder device 40 includes a cylinder 41 connected to the drilling ship and a piston rod 42 connected to the support ring 30. Generally, a plurality of cylinder devices 40 is arranged along the circumference of the riser 4. The hydraulic device 50 supplies hydraulic pressure to each of the cylinders 41 to raise the piston rod 42, so that the lower riser 4 b connected to the slip joint 20 is tensioned.

The hydraulic device 50 includes an accumulator 51 and a pneumatic container 52. When air is supplied from the pneumatic container 52 to the accumulator 51, oil is supplied into the cylinder 41 by pressure of the air, thereby lifting the piston rod 42.

In the case where the distance between the cylinder 41 and the piston 42 is changed due to vertical movement of the drilling ship by waves, hydraulic pressure supplied to the cylinder 41 by the hydraulic device is controlled to be constant to pull the lower riser 4 b by constant tensile force.

FIG. 3 is a cross-sectional view of a cylinder of a conventional riser tensioner.

A piston seal 43 is disposed between the cylinder 41 and a head 42 a of the piston rod 42 to prevent oil supplied to a lower portion “b” of the cylinder 41 by a hydraulic system from leaking to an upper portion “a” of the cylinder 41 while the piston rod 42 is tensioned.

Since offshore drilling is performed for a long duration, there is a high possibility of oil leakage when the piston seal 43 is worn by reciprocation of the piston rod 42. The leaked oil is gathered in the upper portion of the cylinder 41 above the head 42 a of the piston rod 42. Then, when the amount of leaked oil increases over time and the stroke of the piston rod 42 increases by high waves, the oil gathered in the upper portion “a” of the piston rod 42 imparts compressive force to the piton rod 42 and causes the piston rod 42 to bend when the piston rod 42 moves towards an upper dead point.

Since the riser tensioner is located under the drilling ship, it is usually very difficult to detect oil leakage. Further, since the cylinder is dissembled from under the drilling ship to repair the cylinder in the event of oil leakage from the cylinder, the conventional riser tensioner has a problem in that it takes a long time to repair the cylinder. Moreover, when the riser tension is not properly operated due to excessive oil leakage, there is a high possibility of a large accident such as riser buckling and the like.

Therefore, there is a need for a detector capable of detecting oil leakage when oil leaks to the upper portion “a” of the cylinder 41 due to abrasion of a piston seal 43.

Further, there is a need for a mechanism for discharging leaked oil from the cylinder 41 to collect the leaked oil when oil leaks to the upper portion “a” of the cylinder due to abrasion of the piston seal 43.

A riser tensioner disclosed in US Patent Publication No. 2007/0056739 (publication date: Mar. 15, 2007) cannot collect oil leaking through a seal member of a piston rod. Further, JP Unexamined Patent Publication No. 2002-021033 (publication date: Jan. 23, 2002) discloses a garbage truck capable of collecting oil leaking therefrom, but has a problem in that oil gathered in a cylinder cannot be discharged from the cylinder.

BRIEF SUMMARY

The present disclosure is directed to solving the problems of the related art as described above, and an embodiment of the present disclosure provides a riser tensioner that includes a detector capable of detecting oil leakage due to abrasion of a piston seal disposed between a cylinder and a piston rod, and an oil collecting means capable of discharging leaked oil from the cylinder to collect the leaked oil.

In accordance with one aspect of the present disclosure, there is provided a riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied. The riser tensioner further includes: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; and an oil collection passage extending from the head of the piston rod to an outside of the cylinder through the piston rod to allow oil leaking into the cylinder through the piston seal to be discharged from the cylinder to the outside of the cylinder through the oil collection passage.

The oil collection means further includes a collection tank connected to the oil collection passage and storing collected oil.

The collection tank may be provided with an oil leakage detection sensor which detects oil leakage.

As such, the riser tensioner according to the present disclosure includes the oil collection means that discharges oil leaking into the cylinder through the piston seal to collect the leaked oil, and the leakage detection sensor capable of detecting oil leakage, so that, when oil leaks through the piston seal, the oil is discharged from the cylinder as soon as oil leakage is detected, thereby preventing the leaked oil from negatively influencing operation of the riser tensioner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional drilling ship floating on a sea surface for drilling operation;

FIG. 2 is an enlarged view of Part A in FIG. 1;

FIG. 3 is a schematic sectional view of a cylinder of a conventional riser tensioner; and

FIG. 4 is a sectional view of a riser tensioner including an oil collection means in accordance with one exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Herein, like elements will be denoted by like reference numerals throughout the accompany drawings.

FIG. 4 is a sectional view of a riser tensioner including an oil collection means in accordance with one exemplary embodiment of the present disclosure.

Generally, a riser tensioner refers to a device that is connected to a drilling ship to tension a riser in order to prevent the riser from buckling upon movement of the drilling ship by waves during drilling for submarine resources. Herein, the drilling ship means any kind of offshore floating structure for drilling of submarine resource, such as drill ships, rigs, semi-submersible rigs, tension leg platforms, and the like.

A riser tensioner 100 according to one exemplary embodiment is also configured to tension the riser by allowing a piston rod 120 to be pulled by hydraulic pressure supplied to a cylinder 110. Operation of fluid inside the cylinder 110 of the riser tensioner 100 is the same or similar to that of the related art, and a detailed description thereof will thus be omitted.

The riser tensioner 100 includes the cylinder 110, the piston rod 120, a piston seal 130, an oil collection means 140, 150, and a leakage detection sensor 160.

Oil is introduced into the cylinder 110 and generates hydraulic pressure to raise the piston rod 120 in a direction indicated by an arrow.

The piston rod 120 is partially inserted into the cylinder 110 to reciprocate within the cylinder 110 by hydraulic pressure inside the cylinder 110 or by movement of the drilling ship due to waves. The piston rod 120 has a T shape and is provided at an upper portion thereof with a head 120 a.

The piston seal 130 is disposed between the head 120 a of the piston rod 120 and a wall of the cylinder 110 to provide hydraulic sealing and restrict movement of the oil flowing into the cylinder 110, so that hydraulic pressure is generated in the cylinder 110.

Since offshore drilling is performed for a long duration, oil can leak through the piston seal 130 in the case where the piston seal 130 is worn out due to continuous reciprocation of the piston rod 120. The leaked oil is gathered in an upper portion of the cylinder 110 above the head 120 a of the piston rod 120. Then, the amount of leaked oil increases over time and the oil gathered in the upper portion of the piston rod imparts compressive force to the piston rod 120 when the piston rod 42 moves towards an upper dead point, causing negative influence on reciprocation of the piston rod 120.

Thus, according to this embodiment, the riser tensioner includes the oil collecting means which collects leaked oil by discharging the leaked oil from the cylinder 110 when the oil leaks to an upper portion of the cylinder 110 through the piston seal 130.

The oil collecting means may be realized in any shape so long as it can collect leaked oil by discharging the leaked oil from the cylinder 110 when the oil leaks to the upper portion of the cylinder through the piston seal 130.

In one embodiment, the oil collecting means includes an oil collection passage 140 extending downwards from the head 120 a of the piston rod 120 through the piston rod 120, and a collection tank 150 connected to the oil collection passage 140 and storing oil collected therein.

The oil collection passage 140 may be a fluid passage formed through the piston rod 120 from the center of the head 120 a of the piston rod 120. The oil collection passage 140 is connected to the collection tank 150 through a connection passage 141.

The leaked oil flows into the collection tank 150 through the oil collection passage 140 and the connection passage 141. The collection tank 150 may be positioned at any suitable position. The collection tank 150 may be provided with an oil leakage detection sensor 160 which detects oil leakage. The oil leakage detection sensor 160 may be a level sensor which determines oil leakage when the collection tank 150 is filled with a predetermined amount of oil. The oil leakage detection sensor 160 may be positioned at any suitable position, for example, on the head 120 a of the piston rod 120 as well as inside the collection tank 150.

As such, the riser tensioner 100 according to this embodiment includes the oil collecting means 140, 150, which collects leaked oil by discharging the leaked oil from the cylinder 110 when the oil leaks into the cylinder 110 through the piston seal 130, and the leakage detecting sensor 160 which detects oil leakage. Thus, when oil leaks through the piston seal 130, the riser tensioner discharges the oil from the cylinder as soon as oil leakage detected, thereby preventing the leaked oil from negatively influencing operation of the riser tensioner.

Generally, considering that the riser tensioner is located under a drilling ship, causing a difficulty in approaching the riser tensioner and a long time in repair of the riser tensioner, the riser tensioner including the oil collecting means and the leakage detecting sensor 160 according to the embodiment serves as a sufficient safety mechanism in emergency.

In the riser tensioner according to the embodiments of the present disclosure, it is apparent to those skilled in the art that the oil leakage detector, the oil collecting means and the leakage sensor may be realized in various ways.

The embodiment described above can be combined to provide further embodiments. All of the patents, patent application publications, patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiment can be modified, if necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and the claims, but should be construed as including all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A riser tensioner disposed under a drilling ship to tension a riser used for drilling operation of submarine resources and including a plurality of cylinders into which oil is supplied, the riser tensioner further comprising: a piston rod partially inserted into each of the cylinders and reciprocating within the cylinder; a piston seal disposed between a head of the piston rod and a wall of the cylinder to provide fluid sealing therebetween; an oil collection passage extending from the head of the piston rod to an outside of the cylinder through the piston rod to allow oil leaking into the cylinder through the piston seal to be discharged from the cylinder to the outside of the cylinder through the oil collection passage; and a first oil leakage detection sensor configured to detect oil leakage in the piston seal and located on the head of the piston rod.
 2. The riser tensioner of claim 1, further comprising: a collection tank connected to the oil collection passage and configured to store collected oil.
 3. The riser tensioner of claim 2, wherein the collection tank is provided with an a second oil leakage detection sensor configured to detect oil leakage. 